A bridge which has fallen into disrepair is being demolished and replaced to help make way for the Borders to Edinburgh railway line.
It is estimated it will take a week to complete the works on the Cowbraehill Bridge north of Stow.
South of Scotland SNP MSP Christine Grahame said the move showed commitment to delivering the £295m project.
The scheme to link Tweedbank to Edinburgh by rail is due to be completed in 2014.
Scottish Borders Council is undertaking the work on behalf of Transport Scotland and the materials will be reused and recycled on the project.
Stone removed from Cowbraehill will be stored and provided to the main contractor, when appointed, to be used for repair and refurbishment of other bridges along the route.
Other materials will be recycled and used by SBC on other projects.
Ms Grahame said: "The reinstatement of this railway is a vital infrastructure investment that will result in new jobs, new housing and new opportunities for the people of the Borders.
"As this latest announcement demonstrates, work continues to progress steadily and on schedule."
However, Lib Dem MSP Jeremy Purvis said he still had concerns despite the work getting under way.
He has called on the Scottish government to sign the main construction contracts for the Borders rail link before the next Holyrood elections in May.
Mr Purvis said he did not believe the project was under threat because of the squeeze on capital spending.
However, he fears a change in administration at the Scottish Parliament could put the line under threat.